Sunday, 29 May 2016

A good days radio

After a short walk and buying a few books, then picking mother up this morning, and doing a bit of gardening, I found I had time to get a bit of radio work done. Also, the replacement CIARL knob and decals for the RT-351 arrived in the post,

So, I cracked on with replacing the decals. The old original ones peeled off with the aid of a pair of pliers, but the glue underneath took rather a lot of scraping to remove. The spaces left then also had to be painted over. I had decals for the RT-351, all but the rear audio connector plate, which was in good enough condition anyway, the 20W amp, and a few spare MOD Record stickers.

One of the MOD Record ones went onto the LiPo battery pack. This got its first full charge today, in balance mode, and at relatively low current. Either way, I was taking no chances with it

But the 7A 12v PSU and the Turnigy Accucel-8 charger coped just fine. Whilst this was charging, I had the first go at modding the RT-351 for equal mic gain in both Whisper and Loud modes.

After studying the service manual, I came to the conclusion that the easiest way to do this would be to link the 0vW line to ground at the mode switch. That mod can be seen below, the purple wire.

Now, this did indeed work, and as a proof of concept was fine. The trouble was that by grounding this line, it put the extra 20dB mic amp on permanently. This is fine in Whisper mode, but in Loud mode there is awful feedback on the handset due to the mic picking up the sidetone! Of course I could have disabled the sidetone, but I kind of like it, it keeps the set authentic.

But it did prove that the mic gain and hence the Tx deviation level could be made the same between modes. So it was obvious that to do this without invoking the 20dB amp, would simply need the contact on the switch disconnecting.

As can be seen in the above photo, ive done this by desoldering the pad, insulating the pin, and then paring back the track a little. This was actually rather awkward, and required removing the switch from the case AND from the felxi-PCB! I would suggest to anyone else doing this mod to just use a scalpel and cut the track! After all, it can easily be reconnected with a linking wire if needed.

But, I now have an RT-351 where the mic gain and Tx deviation are the same and Whisper and Loud modes are now just volume control! One difficulty though is that this radio does not go into limit on over deviation like many PMR sets, so you can still over or under drive it, depending on how loud you talk, and so setting the deviation isnt easy. Ive done it on the Marconi 2955 with the old 'ooowww-lahhh' trick, to about 3-4kHz, but on air reports will be needed to see if further adjustment is required.

During all this, I also removed the SO-239 antenna connector from the roof of my car, which has yet again gone intermittent and to be honest is knackered, and replaced it with a 3/8" thread bulkhead connector. This means no need anymore for failure prone adapters either. The installation isnt yet usable, as I still need to put a right angle PL-259 plug on the coax and connect the antenna mount to the radio. Im hoping to get that done tomorrow.

And so it was back to the RT-351 and 20W amp, and the stickers. The paint now being dry. Im not sure if these were meant at some time to have been self adhesive, if so they dried out long ago (these spares are probably almost as old as the radios, and some of those are knocking on 35 years!), but some UHU impact adhesive soon sorted that out. Front and back views of the newly labeled radio are below, with the 4W SURF in place and the LiPo battery.

And below, the completely refurbished PRC-352 system, comprising Handset, 1.2m whip antenna, 4W SURF (Selective Unit Radio Frequency), RT-351 4W VHF FM transceiver, 20W amplifier, 24v 4Ahr NiCd battery, Adapter plate and GS carrier frame. The 10m select toggle switch can be seen on the left where the dessicator plug used to be.

I also found time to convert a DCCU charging cable for the 24v NiCds into an Accucel-8 charging cable for the 24v NiCds! This makes charging them much more convenient, and as the Accucel-8 can do discharge/charge cycling for battery conditioning, should help keep them in good order.

And now, late at night, im just waiting for the last battery to finish charging before I turn in, and have got some way to converting a cheap D-type RS232 to TTL converter into a programming lead for the Yaesu VX-2000.

Friday, 27 May 2016

Amateurizing the PRC-351?

I mentioned in my last post that suitability for amateur use of the PRC-351 is somewhat limited by the way the Loud/Whisper audio system works, and how I planned to look into setting the Tx deviation up in such a way as to make it more usable on both settings.

Now, theres a few problems with this. The first is to understand how the two level systems operate. On receive, in Loud mode, a two stage amplifier is at work. In Loud mode, pin 5 of module 7 is grounded, to enable both stages. In Whisper mode this pin is not grounded, which disables the stage and reduces the gain by 20dB. On transmit, the mic amplifier module 13 pin 9 is floating when in Loud mode, and so the mic gain is standard, but is grounded in Whisper mode, enabling an additional 20dB amplifier.

The result is that in Whisper mode, the earpiece audio is quiet, and the mic gain is high. In Loud mode, the earpiece audio is increased, but the mic gain is lower.

Now, what we need to do is have the same mic gain level in both Whisper and Loud mode, whilst maintaining the two different levels on the receive side. As it happens, the two control lines for module 13 pin 9, and module 7 pin 5 (and in fact the 'noise on' control line, which is concurrent with the Loud command) are sourced directly from the mode switch itself. And, as luck would have it, it seems that they are independent!  If we examine the mode switch, 2S1, we see that this is a 3-pole 4-way rotary switch. In the OFF position, all three poles go to unused contacts. In any of the three ON positions, one of the poles connects the battery supply through, whilst the other two poles control the audio command lines.  One of these poles has only one contact connected, which provides the Noise On signal. The remaining pole controls the audio mode. In Whisper mode, the control line to module 13 pin 9 is grounded, but the lines to module 7 pin 5 are untouched. In Loud and Noise On modes, the control line to module 13 pin 9 is left floating, and the line to module 7 pin 5 is grounded.

Now, unless somewhere else also uses the same control line, it seems that in order to make the mic amp operate as in Loud mode all the time, whilst retaining the two options for the receive audio, all that is needed is to disconnect the contact for that line from the switch! And, this line is much more easily accessible at the switch than at the modules! If it happens that the extra gain is needed to allow the deviation to be set as required, then simply adding a permanent ground line to this contact will fix that. In fact, this would be the easiest trick to try first, requiring just a small jumper wire!

The second problem, is that this radio uses two VCO's, one for the lower band and one for the higher band, and as the set uses reaction modulation of the VCO frequency, there are two deviation controls to adjust! Not an insurmountable problem.

I need now to study the schematic and make sure that the '0v W' line as its notated, only goes to just pin 9 on module13.

Wednesday, 25 May 2016

Clansman RT-351 Refurb and Mod

I had planned a very busy day today - a bit of radio work, and lots of gardening. But, its not stopped raining all day, so instead the hours have been spent in the workshop continuing with the Clansman refurbishment.

So first the outer case sleeve of the RT-351 got its second coat. Although i'd masked the labels on this, they are likely to be coming off anyway, as ive ordered nice shiney new ones. I will transfer the serial numbers over, and also engrave my callsign on them!

I also decided that, since dismantling the -351 is such a bloody ball-ache, I would carry out the 10m modification whilst I was about it. This involved removing all the electronics from the chassis. But then I had to do that anyway in order to paint all the casings.

With everything dismantled, came the delicate and scary task of modifying the flexible PCB. This as can be seen below connects everything in these sets together, and can become brittle with age and risk cracking, destroying tracks. Well, theres a good chance this set is over 30 years old! So I was taking no chances and handling it very carefully

I had to desolder and lift half of the flexi in order to modify the connection. This gave me a chance to try out my new £1 chinese solder sucker, which did a passable job. With the pads unsoldered I slowly expanded the hole for synthesiser pin 15 using small drill bits. The white wire was soldered to pin 15 and insulated from the surrounding PCB flexi pad with heat shrink. The pad then had the pink wire soldered to it. Finally, a grey wire for the ground connection was added, and the flexi replaced and resoldered.

In order to install the toggle switch to select 10m, I had to remove the drying plug and drill out the thread. This was a pig! It turns out the thread is a carbon steel insert! I'd painted the casing by this time and reinstalled the control knobs.  The switch can be seen in the photo below. Once they come from China the nut will be replaced with a waterproof rubber boot. This will be much more in keeping with the style of the radio, which is generally devoid of chrome.

With the mode done, the switch installed, and the paint dry, I began to reassemble the unit. Here I realised a problem - the switches have no end stops! I couldnt align the knobs and switches. Any other equipment i'd have winged it and just redone them if wrong, but thats not a good option here where its a real bitch to put together, and each time it has to be opened risks damage. I eventually discovered that each switch has two tiny dots molded on it, and when these are aligned, the 25kHz, 100kHz and 1MHz switches are all set to zero. The 10MHz switch when these dots align is set to 3. I had to resort to metering out the connections to discover that about the 1MHz switch! Essentially, with the knobs set to 30.000MHz, and the switches all with the dots aligned, they all fit together.

So, I reassembled the radio - and it didnt work!

Ok, so it kind of worked. As I tested the switches one of them slipped before starting to click, this was the 1MHz. I soon discovered that the setting was 5MHz out. I had to take it all apart again! But this time, I was more careful and the switches all aligned properly. There were just two problems now - abysmal modulation and no rx audio! This was down to poor earth from the audio module, solved by reinstalling the back part of the case.

Time to test the mod! I set the frequency, flipped the switch - Dead! No Rx, No Tx!

It took me reading the service manual, the operators manual, and taking Sam to karate and back to realise what was wrong! I'd set the wrong frequency! The mod fools the synth into setting the tens of MHz divider to 20MHz and not 30MHz. I'd set 36.9MHz, which gave 26.9MHz - well out of VCO lock range! I should have set 39.6MHz! That gives 29.600MHz - the 10m FM calling frequency. I'd just got the 6 and 9 the wrong way around!

With 39.600 set on the dials, I flipped the mod switch - perfect reception and transmission on 29.6MHz! A bit of checking revealed that the set now will lock right down to 27.750MHz!!!

Before putting it all back together, I want to look at doing one final mod - setting the Tx deviation to +/- 5kHz on both W and L audio settings, thus making my Tx signal good on both and making it just a volume control.

I also rebuilt and tested the newly pained RT-320, this is essentially finished now. The LiPo battery pack has got a coat of fresh paint, thats still drying.

And the GS carry frame and adapter plate are finished and the straps replaced. 

A few more days and the Clansman system will all be refurbished.

Sunday, 22 May 2016

Lyke Wake Walk - Reverse Route - charity challenge 2016

Those of you who regularly read this blog and my others will know that Im a long distance walker with a penchant for charity walks that almost kill me,

This year myself and Bob M1BBV are again doing the Lyke Wake for charity, only this time backwards! (that is, the route backwards, but walking forwards! were not THAT mad!)

If you would like to support us and our charity, Meningitis Now, just click here and donate!

Deep Bronze Green - Everywhere!

Yesterday, when I had a huge number of jobs to do on the veg patch, it absolutely pissed it down almost all day. So, instead of weeding the veggies, I painted Clansman radios.

Before I write about that though, i'll just put up this link...

How I connected the Frequency Counter

Ive had quite a few emails recently asking about how I added the Frequency Counter module to the Chinese Airband Receiver kit. Since the only place I talk about that kit is on the blog, clearly these enquiries have come from here, so if you are wondering how I did it, follow the link above which will take you to the blog entry detailing the connections.

So, on with the painting! I pinched a couple of Julies new brushes in order to start with this. As well as the radios and ancilliaries, the carry frame for the PRC-351/2 also needed some serious work. So I started by removing all the straps and fittings, and taking the adaptor plate off.

Ther frame itself just needed a bit of a go over with a wire brush in places, before a good coat of paint. Its now sat drying on a couple of wooden blocks

The rest was not so easy! The adaptor plate needed quite a bit of peeling paint removing, as well as the coax link cable for the amp block. This is also now sat on the wooden blocks.

I did have one disaster though - it turns out the control knobs of the RT-351 are not friction fit as I thought, but held on at the back of the panel with circlips. I now require a replacement mode knob! In order to remove the knobs the entire radio has to be totally stipped down, not a nice task on flexi-pcbs nearly 40 years old!

The innards of the -351 are now on the bench with yet another 'Do Not Touch' sign on them. The main casing, along with the main case of the RT-320, and the 20w amp and 4w SURF, are all drying on the work bench

The -320 is the priority, as its planned to use that up on Snowdon in a week or so's time! To make that easier, and to keep the radio safe, ive acquired a new (or at least grade A1) radio bergen!

This will also be used for the Lions Mid-Summer Walk in June, all I have to do now is get the form back to Ofcom, and decide on the best frequencies to use!

Friday, 20 May 2016

Well, what a knob!

Having decided I was happy with the paint finish on the RT-320, and having mostly rebuilt the radio into the front panel, I managed over the last few days to complete the rebuild of the ATU, and put the radio on test...

Bugger! It seems that although the coupler for the turret tuner can only fit to the tuner in one way, the control shaft can fit to the coupler the wrong way around!

I now have a radio where the band select knob points 180 degrees opposite to the selected band!

So, it looks like i'll be dismantling it again. Hopefully I can get away with just releasing the turret unit enough to turn the knob around!

Monday, 9 May 2016

Some small jobs, and a scary bit

With a few free hours on a nice weekend, I managed to find time to get a bit of radio work done, at least, enough to progress a couple of 'commission' jobs a little.

One of these is a ruggedised 9v power regulator for Bob M1BBV. A simple enough circuit

Much of the work needed for this is metal bashing. Above is the view with the LEDs and fuse holders installed, and the 7809 9v positive regulator.

Built 'dead bug' style, using a couple of bolts and solder tags to ground as stand-offs, but otherwise hard wired between the legs and terminals of the various devices. A red LED indicates that the input 12v supply is good after the first fuse (protects the batteries, also includes an 'idiot diode' just for Bob!), and the green LED indicates the output 9v is good.

Above is the completed unit. The device has flying leads rather than chassis connectors so Bob can use whatever crimps or the like he wishes.

A bit more work was also done to the Theremin, including adding the oscillator FETs and the volume control. Just the antennas needed now and I can start testing and alignment.

Having been instructed by my good lady wife that I had to clean the front gutters out, which means working up the ladders, I decided after completing that task to finally finish putting the brackets up for the antenna pole on the side of the house. Just to get all the work at height done and out of the way whilst I was still in a state of abject terror. This involved using a pnumatic hammer drill and a big 16mm SDS at over 30ft, something I was not particularly happy about, but the brackets are now installed, after a mere six or so years.

And ive also finally started to rebuild the RT-320. Happy with the new paint finish, I started to reinstall the radio last night - i'd only popped out to check everything was turned off in the workshop!
But, all but the ATU is now remounted to the front panel, although the nuts still need tightening. And I only managed to trap one wire! I just hope ive reconnected the power wiring correctly, as I really dont like the very small insulated bushing that bolts the solder tags down to the casing!

Tuesday, 3 May 2016

Going Slow

Not much doing radio wise at all at the moment. Other things to do.

Have given the RT-320 front panel its second coat today though. A bit more work and i'll be able to start rebuilding the 'good' radio - at least, getting the front panel mounted back on and the radio in a state where it can be made operational.